Heat pump type hot water supplying device

ABSTRACT

The present invention provides a heat pump type hot water supplying device that has solved the inconvenience of an antifreeze operation being not carried out due to the phenomenon of a backflow from a hot water storage tank without increasing the number of components. A control device  70  carries out an antifreeze operation, in which a water pump  23  is operated, if the temperature of water for hot water supply in a hot water supply circuit  20  positioned in a heating unit  50  decreases to a predetermined value or less. The water pump  23  is operated if the temperature of the water for hot water supply in the hot water supply circuit  20  positioned in the heating unit  50  increases while the water pump  23  is in a stopped state.

TECHNICAL FIELD

The present invention relates to a heat pump type hot water supplying device adapted to heat water for hot water supply in a hot water storage tank by a heat pump circuit.

BACKGROUND ART

Hitherto, as this type of heat pump hot water supplying device, there has been known one that includes a tank unit incorporating a hot water storage tank that stores water for hot water supply, a hot water supply circuit in which the water for hot water supply in the hot water storage tank is taken out from a lower part of the hot water storage tank by a pump, circulated into a water heat exchanger through an inflow pipe, and led into an upper part of the hot water storage tank through an outflow pipe, and a heating unit incorporating a heat pump circuit that heats, by a refrigerant, the water for hot water supply which circulates through the water heat exchanger of the hot water supply circuit (refer to, for example, Patent Document 1).

Further, the inflow pipe and the outflow pipe of the hot water supply circuit described above are usually insulated. If the insulation is insufficient or in an environment in which the outside air temperature becomes extremely low during a winter season or the like, there have been cases where the water for hot water supply in the inflow pipe or the outflow pipe of the hot water supply circuit described above inconveniently freezes. If the water for hot water supply freezes in the inflow pipe or the outflow pipe, then the water for hot water supply cannot be circulated through the hot water supply circuit even when a pump is actuated, eventually causing frost to build up on an evaporator in the heating unit. This in turn inconveniently causes an air blower to hit the frost, damaging the air blower.

Conventionally, therefore, an antifreeze operation has been carried out, in which, if an inflow water temperature sensor, which detects the temperature of the water for hot water supply on the inflow side of the water heat exchanger provided in the heating unit (an inflow water temperature detecting means), detects a predetermined low temperature (the predetermined value being higher than a freezing point), then the high-temperature water for hot water supply (hot water) in the hot water storage tank is circulated into the hot water supply circuit by operating a pump (refer to, for example, Patent Document 2).

CITATION LIST Patent Documents

-   Patent Document 1: Japanese Patent Application Publication No.     2013-76512 -   Patent Document 2: Japanese Patent Application Publication No.     2014-196849

SUMMARY OF THE INVENTION Problems to be Solved by the Invention

In many cases, a heating unit is installed on the roof of a house or the like, while a tank unit is installed in a basement of a house or on the ground outside the house. In such an installation condition, the heating unit is positioned higher than the tank unit. Hence, while a pump is in a stopped state, if the outside temperature decreases and the temperature of the water for hot water supply in the outflow pipe decreases during a winter season or the like, then a phenomenon occurs, in which the high-temperature water for hot water supply (hot water) at the upper part in the hot water storage tank flows backward into the outflow pipe due to a difference in density.

If such a backflow phenomenon occurs, then the temperature of the outflow pipe increases, eventually causing the temperature of the hot water supply circuit positioned in the heating unit to also increase. This disables the inflow water temperature sensor, which is adapted to detect the temperature of the water for hot water supply on the inflow side of the water heat exchanger, to detect the foregoing predetermined value, so that the antifreeze operation is no longer carried out.

However, the temperature of the inflow pipe positioned between the heating unit and the tank unit does not increase, so that the water for hot water supply in the inflow pipe, the temperature of which is low from the beginning, inconveniently freezes. This has led to the inconvenience of impeding the circulation of the water for hot water supply in the hot water supply circuit. As a means for preventing the backflow phenomenon, a check valve (the forward direction thereof being the direction of the hot water storage tank) or the like could be installed in the outflow pipe. This, however, adds to the number of components, leading to an increase in cost.

The present invention has been made to solve the technological difficulties of the conventional art described above, and an object of the invention is to provide a heat pump type hot water supplying device which has solved the inconvenience of an antifreeze operation failing to be performed due to the phenomenon of a backflow from a hot water storage tank without increasing the number of components.

Means for Solving the Problems

A heat pump type hot water supplying device in accordance with the present invention includes: a heating unit provided with a heat pump circuit formed by connecting a compressor, a water heat exchanger, a decompressor and an evaporator; a tank unit provided with a hot water storage tank for storing water for hot water supply; a hot water supply circuit in which the water for hot water supply in the hot water storage tank is taken out from a lower part of the hot water storage tank by a water pump, circulated into the water heat exchanger and then led into an upper part of the hot water storage tank; and a control device which carries out a boiling operation for heating, by a refrigerant, the water for hot water supply, which circulates through the water heat exchanger, by operating the water pump and the compressor, wherein the control device carries out an antifreeze operation, in which the water pump is operated, in the case where the temperature of the water for hot water supply in the hot water supply circuit positioned in the heating unit decreases to a predetermined value or less, and also operates the water pump in the case where the temperature of the water for hot water supply in the hot water supply circuit positioned in the heating unit increases while the water pump is in a stopped state.

According to the heat pump type hot water supplying device of the invention of claim 2, the control device operates the water pump in the case where the temperature of the water for hot water supply in the hot water supply circuit positioned in the heating unit temporarily decreases and then switches to increase while the water pump is in a stopped state in the foregoing invention.

According to the heat pump type hot water supplying device of the invention of claim 3, the control device operates the water pump in the case where the temperature of the water for hot water supply in the hot water supply circuit positioned in the heating unit increases by a predetermined value or more within a predetermined time while the water pump is in a stopped state in the foregoing inventions.

According to the heat pump type hot water supplying device of the invention of claim 4, the control device operates the water pump in the case where an outside air temperature is a predetermined value or lower and the temperature of the water for hot water supply in the hot water supply circuit positioned in the heating unit increases while the water pump is in a stopped state in the foregoing inventions.

According to the heat pump type hot water supplying device of the invention of claim 5, the control device operates the compressor in the case where the temperature of the water for hot water supply on an inflow side of the water heat exchanger is a predetermined low value despite the water pump having been operated for a predetermined time in an antifreeze operation in the foregoing inventions.

According to the heat pump type hot water supplying device of the invention of claim 6, the control device carries out the antifreeze operation in the case where the temperature of the water for hot water supply in the hot water supply circuit positioned in the heating unit increases while the water pump is in a stopped state in the foregoing invention.

According to the heat pump type hot water supplying device of the invention of claim 7, the temperature of the water for hot water supply in the hot water supply circuit positioned in the heating unit is the temperature of the water for hot water supply on the inflow side of the water heat exchanger or the temperature of the water for hot water supply on the hot water outflow side of the water heat exchanger in the foregoing inventions.

According to the heat pump type hot water supplying device of the invention of claim 8, the heating unit is disposed at a position that is higher than the position of the tank unit in the foregoing inventions.

According to the heat pump type hot water supplying device of the invention of claim 9, the hot water supply circuit has the inflow pipe, which is positioned between the heating unit and the tank unit to take out the water for hot water supply in the hot water storage tank from the lower part of the hot water storage tank, and the outflow pipe for passing the water for hot water supply, which has circulated through the water heat exchanger, into the upper part of the hot water storage tank, wherein at least a part of the inflow pipe and the outflow pipe is provided at a position that is higher than the position of the tank unit in the foregoing inventions.

Advantageous Effect of the Invention

According to the present invention, the heat pump type hot water supplying device includes: the heating unit provided with the heat pump circuit formed by connecting the compressor, the water heat exchanger, the decompressor and the evaporator; the tank unit provided with the hot water storage tank that stores water for hot water supply; the hot water supply circuit in which the water for hot water supply in the hot water storage tank is taken out from the lower part of the hot water storage tank by the water pump, circulated into the water heat exchanger and led into the upper part of the hot water storage tank; and the control device which carries out the boiling operation for heating, by a refrigerant, the water for hot water supply, which circulates through the water heat exchanger, by operating the water pump and the compressor. When the control device carries out the antifreeze operation, during which the water pump is operated, in the case where the temperature of the water for hot water supply in the hot water supply circuit positioned in the heating unit, e.g. the temperature of the water for hot water supply on the inflow side of the water heat exchanger as in the invention of claim 7, or the temperature of the water for hot water supply on the hot water outflow side of the water heat exchanger decreases the predetermined value or lower, the control device operates the water pump if the temperature of the water for hot water supply in the hot water supply circuit positioned in the heating unit increases while the water pump is in a stopped state. Hence, the water for hot water supply can be circulated in the hot water supply circuit by operating the water pump in the case where the phenomenon of backflow of the high-temperature water for hot water supply (hot water) from the hot water storage tank occurs in the hot water supply circuit.

This arrangement makes it possible to prevent the inconvenience in which the antifreeze operation is not carried out and the hot water supply circuit freezes due to the backflow phenomenon, which tends to occur in the case where the heating unit is disposed at a position that is higher than the position of the tank unit, as in, for example, the invention of claim 8, or in the case where at least a part of the inflow pipe and the outflow pipe of the hot water supply circuit is provided at a position that is higher than the position of the tank unit, as in the invention of claim 9. Further, it is no longer required to provide the hot water supply circuit with a check valve or the like, thus making it possible to prevent an increase in cost attributable to an increased number of components.

Further, according to the invention of claim 2, in addition to the foregoing invention, the control device operates the water pump if the temperature of the water for hot water supply in the hot water supply circuit positioned in the heating unit temporarily decreases and then switches to increase while the water pump is in the stopped state. Hence, the occurrence of the backflow phenomenon that takes place after the water pump stops can be accurately determined.

Further, according to the invention of claim 3, in addition to the foregoing inventions, the control device operates the water pump if the temperature of the water for hot water supply in the hot water supply circuit positioned in the heating unit increases by the predetermined value or more within the predetermined time while the water pump is in the stopped state. Hence, the occurrence of the backflow phenomenon can be further accurately determined.

Further, according to the invention of claim 4, in addition to the foregoing inventions, the control device operates the water pump if the outside air temperature is the predetermined value or lower and the temperature of the water for hot water supply in the hot water supply circuit positioned in the heating unit increases while the water pump is in the stopped state. This makes it possible to accurately detect the backflow phenomenon in a low outside air temperature environment so as to avoid unnecessary operation of the water pump.

The prevention of freezing of the hot water supply circuit can be further smoothly accomplished by the control device operating the compressor in the case where the temperature of the water for hot water supply on the inflow side of the water heat exchanger is the predetermined low value even after the water pump is run for the predetermined time in the antifreeze operation, as in the invention of claim 5. The freezing of the hot water supply circuit in the case where the backflow phenomenon occurs can be further reliably prevented if the control device carries out the antifreeze operation also when the temperature of the water for hot water supply in the hot water supply circuit positioned in the heating unit increases while the water pump is in the stopped state, as in the invention of claim 6.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a configuration diagram of a heat pump type hot water supplying device as an embodiment to which the present invention has been applied;

FIG. 2 is a flowchart of a boiling operation carried out by a control device of the heat pump type hot water supplying device of FIG. 1; and

FIG. 3 is a flowchart of an antifreeze operation (including a backflow determination process) carried out by the control device of the heat pump type hot water supplying device of FIG. 1.

MODE FOR CARRYING OUT THE INVENTION

The following will describe in detail an embodiment of the present invention with reference to the accompanying drawings.

(1) Heat Pump Type Hot Water Supplying Device 1

A heat pump type hot water supplying device 1 according to the embodiment includes a hot water storage tank 10, which stores water for hot water supply, a hot water supply circuit 20, which circulates the water for hot water supply of the hot water storage tank 10, a heat pump circuit 30, which circulates a refrigerant, and a water heat exchanger 40, which performs heat exchange between the water for hot water supply of the hot water supply circuit 20 and the refrigerant of the heat pump circuit 30. The heat pump type hot water supplying device 1 is adapted to heat the water for hot water supply circulating through the hot water supply circuit 20 by the refrigerant of the heat pump circuit 30.

(2) Hot Water Storage Tank 10

The hot water storage tank 10 is formed of a vertically long, hermetically sealed vessel, and is installed on the ground outside a house or in a basement or the like. A water supply pipe 11 for introducing tap water is connected to a lower part of the hot water storage tank 10. Further, the water supply pipe 11 is provided with a pressure reducing valve 12. Connected to an upper part of the hot water storage tank 10 is a hot water supply pipe 13 for supplying the hot water in the hot water storage tank 10 to a hot water supply destination in a house, the hot water supply pipe 13 and the water supply pipe 11 being connected through a bypass pipe 14.

A mixing valve 15 is provided between the hot water supply pipe 13 and the bypass pipe 14. The mixing valve 15 is configured to mix the hot water in the hot water storage tank 10 and the water from the water supply pipe 11 and circulate the mixture through the hot water supply pipe 13. Further, the hot water storage tank 10 is provided with a stored hot water temperature sensor 16, which detects the temperature of the water for hot water supply in the hot water storage tank 10. The stored hot water temperature sensor 16 is installed at a predetermined location in the vertical direction of the hot water storage tank 10 (at approximately the center in the embodiment).

(3) Hot Water Supply Circuit 20

The hot water supply circuit 20 includes an inflow pipe 21 connected between the lower part of the hot water storage tank 10 and an inflow side connection port 52 installed to the outer surface of an exterior case 51 of a heating unit 50, which will be discussed later, a water pump 23, an inflow water pipe 22 connected between the inlet side of the water pump 23 and the connection port 52, an outflow water pipe 24 connected between a discharge side of the water pump 23 and the inflow side of the water heat exchanger 40, a hot water outflow pipe 26 connected between the outflow side of the water heat exchanger 40 and an outflow-side connection port 54 installed to the outer surface of the exterior case 51, and an outflow pipe 27 connected to the connection port 54 and the upper part of the hot water storage tank 10. The inflow water pipe 22 is provided with an inflow water temperature sensor 28, which detects the temperature of the water for hot water supply taken out of the lower part of the hot water storage tank 10 (the temperature of the water for hot water supply on the inflow side of the water heat exchanger 40), and the hot water outflow pipe 26 is provided with an outflow hot water temperature sensor 29, which detects the temperature of the water for hot water supply after passing through the water heat exchanger 40 (the temperature of the water for hot water supply on the hot water outflow side of the water heat exchanger 40).

The hot water supply circuit 20 is provided with a drain plug 18 for draining the water inside. The drain plug 18 is also provided on the outer surface of the exterior case 51 of the heating unit 50 and connected in communication with the inflow water pipe 22 through a drain pipe 19. Reference numerals 52A and 54A denote air vent valves provided at the connection ports 52 and 54, respectively. Reference numeral 25 denotes a filter provided in the inflow water pipe 22. Further, reference numeral 55 denotes an outside air temperature sensor, which is installed inside the exterior case 51 and which detects an outside air temperature.

(4) Heat Pump Circuit 30

The heat pump circuit 30 is composed of a refrigerant circuit formed by connecting a compressor 31, the water heat exchanger 40, an expansion valve 33 acting as a decompressor, and an evaporator 32, and is configured such that a refrigerant is circulated in the order of the compressor 31, the water heat exchanger 40, the expansion valve 33, the evaporator 32, and the compressor 31. The refrigerant used for the heat pump circuit 30 is a natural refrigerant, such as CO₂ (carbon dioxide). Further, reference numeral 34 denotes an air blower for blowing outside air to the evaporator 32.

The water heat exchanger 40 is composed of a double-pipe heat exchanger, which has a refrigerant flow passage 41 and a water flow passage 42. The heat pump circuit 30 is connected to the refrigerant flow passage 41, and the outflow water pipe 24 and the hot water outflow pipe 26 of the hot water supply circuit 20 are connected to the water flow passage 42.

The heat pump type hot water supplying device 1 according to the embodiment includes the heating unit 50 provided with the water pump 23, the heat pump circuit 30, the water heat exchanger 40, the inflow water temperature sensor 28, the outflow hot water temperature sensor 29 and the like, and a tank unit 60 provided with the hot water storage tank 10 and the stored hot water temperature sensor 16. The heating unit 50 and the tank unit 60 are connected at the connection ports 52 and 54 installed to the exterior case 51 of the heating unit 50 through the inflow pipe 21 and the outflow pipe 27 of the hot water supply circuit 20.

The heating unit 50 is frequently installed on the roof of a house or the like. The heating unit 50 in the embodiment is installed on the roof of a house, and the tank unit 60 including the hot water storage tank 10 is installed in a basement. The inflow pipe 21 and the outflow pipe 27 of the hot water supply circuit 20 connecting the heating unit 50 and the hot water storage tank 10 extend for more than ten meters and are installed, being routed upward outside the house toward the heating unit 50 on the roof from the hot water storage tank 10 in the basement.

In the case where the heating unit 50 is installed on the ground outside the house, a major part of the inflow pipe 21 and the outflow pipe 27 connected to the hot water storage tank 10 installed in the basement or the like is frequently routed along an attic or the like (referred to as “right-angled piping”). In this case also, the inflow pipe 21 and the outflow pipe 27 are routed upward for a long distance from the hot water storage tank 10 and then directed downward toward the heating unit 50. Further, the inflow pipe 21 and the outflow pipe 27 are normally insulated by a thermal insulating material (not illustrated) in order to reduce the heat dissipation of the water for hot water supply flowing in the inflow pipe 21 and the outflow pipe 27 and to prevent freezing.

(5) Control Device 70

Further, the heat pump type hot water supplying device 1 is provided with a control device 70, to which the stored hot water temperature sensor 16, the inflow water temperature sensor 28, the outflow hot water temperature sensor 29, the outside air temperature sensor 55, the compressor 31, the air blower 34, and the water pump 23 are connected. The control device 70 is placed in the exterior case 51 of the heating unit 50. The control device includes a CPU (microcomputer), which stores programs, and is configured to control the compressor 31, the water pump 23, and the air blower 34 on the basis of the temperatures detected by the stored hot water temperature sensor 16, the inflow water temperature sensor 28, the outflow hot water temperature sensor 29, and the outside air temperature sensor 55 in the embodiment. Further, the control device 70 has a timer function. Connected to the control device 70 is a remote controller (operation panel) 71 for performing operations, including the setting of the timer function and displaying errors and the like, the remote controller 71 being placed also in the exterior case 51.

(6) Circulation of the Water for Hot Water Supply in the Hot Water Supply Circuit 20

When the water pump 23 of the hot water supply circuit 20 is actuated by the control device 70, the water for hot water supply in the hot water storage tank 10 is taken out from the lower part of the hot water storage tank 10 and directed upward to the roof through the inflow pipe 21. The water for hot water supply that has moved upward through the inflow pipe 21 into the heating unit 50 through the connection port 52 is circulated through a water flow passage 42 of the water heat exchanger 40 via the inflow water pipe 22, the water pump 23 and the outflow water pipe 24, and then passed through the hot water outflow pipe 26 into the outflow pipe 27 through the connection port 54. The water for hot water supply that has entered the outflow pipe 27 moves down in the outflow pipe 27 and flows into the upper part of the hot water storage tank 10.

(7) Circulation of the Refrigerant in the Heat Pump Circuit 30

Further, when the compressor 31 of the heat pump circuit 30 is actuated by the control device 70, the high-temperature refrigerant (carbon dioxide) discharged from the compressor 31 is passed through the refrigerant flow passage 41 of the water heat exchanger 40, thus carrying out the heat exchange between the high-temperature refrigerant of the refrigerant flow passage 41 and the water for hot water supply of the water flow passage 42. This causes the water for hot water supply of the hot water supply circuit 20 to be heated by the water heat exchanger 40. Meanwhile, the temperature of the high-temperature refrigerant decreases by heating the water for hot water supply in the water heat exchanger 40. The refrigerant further passes through the expansion valve 33 so as to expand into a low temperature, low pressure state, thus turning into a gas-liquid two-phase refrigerant. The gas-liquid two-phase refrigerant flows into the evaporator 32 and evaporates. The evaporator 32 is ventilated with outside air by the air blower 34, so that the refrigerant draws up heat from the outside air by the endothermic action of evaporation. Then, the refrigerant that has absorbed heat in the evaporator 32 repeats the cycle of being drawn into the compressor 31.

(8) Boiling Operation

Further, when hot water is used at a hot water supply destination, the water for hot water supply at the upper part of the hot water storage tank 10 flows out into the hot water supply pipe 13 and the amount of water that is equal to the amount of the water for hot water supply that has flowed out is supplied to the lower part of the hot water storage tank 10 through the water supply pipe 11. In other words, the use of the hot water causes the high-temperature water for hot water supply in the hot water storage tank 10 to decrease, while the low-temperature water for hot water supply increases at the lower part of the hot water storage tank 10, so that the temperature detected by the stored hot water temperature sensor 16 will gradually decrease.

The control device 70 determines in step S1 of the flowchart of FIG. 2 whether the temperature detected by the stored hot water temperature sensor 16 has decreased to a predetermined stored hot water temperature T1 or lower. If the hot water in the hot water storage tank 10 is used and the temperature detected by the stored hot water temperature sensor 16 reaches the stored hot water temperature T1 or lower as described above, then the control device 70 proceeds from step S1 to step S2 to start the operations of the compressor 31, the air blower 34 and the water pump 23 thereby to start the boiling operation.

Since the high-temperature refrigerant is passed through the refrigerant flow passage 41 of the water heat exchanger 40, the water for hot water supply passed through the water flow passage 42 is heated and then directed into the hot water storage tank 10. Thus, high-temperature hot water is stored in the hot water storage tank 10. In step S3, the control device 70 determines whether the temperature of the water for hot water supply in the inflow water pipe 22 detected by the inflow water temperature sensor 28 has reached the predetermined inflow water temperature T2 (T1<T2) or higher, and if the temperature is lower than the inflow water temperature T2, then the control device 70 continues the boiling operation. Thereafter, when the temperature detected by the inflow water temperature sensor 28 reaches the inflow water temperature T2 or higher, then the control device 70 proceeds from step S3 to step S4 to stop the compressor 31 and the air blower 34. The water pump 23 continues to run.

Next, the control device 70 proceeds to step S5 to determine whether the temperature of the water for hot water supply in the hot water outflow pipe 26 on the hot water outflow side of the water heat exchanger 40 detected by the outflow hot water temperature sensor 29 has decreased to or below the temperature of the water for hot water supply in the inflow water pipe 22 on the inflow side of the water heat exchanger 40 detected by the inflow water temperature sensor 28. If the temperature detected by the outflow hot water temperature sensor 29 is higher than the temperature detected by the inflow water temperature sensor 28, then the operation of the water pump 23 is continued without interruption and the heat of the water heat exchanger 40 after the compressor 31 stops is recovered.

Thereafter, if the temperature detected by the outflow hot water temperature sensor 29 decreases to or below the temperature detected by the inflow water temperature sensor 28, then the control device 70 proceeds to step S6 to stop the water pump 23 thereby to terminate the boiling operation. Thus, hot water of a predetermined high temperature is stored in the hot water storage tank 10 at all times during the operation.

Even if the temperature detected by the stored hot water temperature sensor 16 does not reach the foregoing stored hot water temperature T1 or lower, the control device 70 actuates the compressor 31, the air blower 34 and the water pump 23 to start the boiling operation when the time counted by the foregoing timer function from the end of a previous boiling operation reaches a predetermined time. Thereafter, the operation of step S3 to step S6 is carried out in the same manner and then the boiling operation is terminated.

The control device 70 carries out the boiling operation for storing the water for hot water supply of the predetermined temperature in the hot water storage tank 10 as described above. The stored hot water temperature sensor 16, which detects the temperature of the water for hot water supply in the hot water storage tank 10, is provided at a predetermined vertical location of the hot water storage tank 10, and the stored hot water temperature sensor 16 is connected to the control device 70, so that the control device 70 carries out the boiling operation on the basis of the temperature detected by the stored hot water temperature sensor 16. This eliminates the need for providing the hot water storage tank 10 with a control device. Thus, a general-purpose product can be used as the hot water storage tank 10, contributing to improved versatility.

(9) Antifreeze Operation (Including the Determination of a Backflow)

Referring now to the flowchart of FIG. 3, the antifreeze operation (including the determination of a backflow) carried out by the control device 70 will be described. As described above, the inflow pipe 21 and the outflow pipe 27, which are routed over a relatively long distance mainly outside a house and which are insulated with an insulating material (not illustrated) in order to reduce the heat dissipation of the water for hot water supply passing therethrough and to prevent freezing. If the insulation is insufficient or in an environment in which the outside air temperature becomes extremely low during a winter season or the like, then the water for hot water supply in the inflow pipe 21 or the outflow pipe 27 of the hot water supply circuit 20 inconveniently freezes.

Therefore, the control device 70 carries out the operation for preventing the inflow pipe 21 and the outflow pipe 27 from freezing. More specifically, while the water pump 23 is at rest, the control device 70 constantly monitors the temperature of the water for hot water supply detected by the inflow water temperature sensor 28, which detects the temperature of the water for hot water supply on the inflow side of the water heat exchanger 40 provided in the heating unit 50, and the temperature of the water for hot water supply detected by the outflow hot water temperature sensor 29, which detects the temperature of the water for hot water supply on the hot water outflow side of the water heat exchanger 40, and determines in step S7 of FIG. 3 whether the temperature detected by the inflow water temperature sensor 28 or the outflow hot water temperature sensor 29 has decreased to or below a predetermined value T3 (a predetermined low temperature that is higher than the freezing point). As is obvious from the flowchart of FIG. 2 described above, while the water pump 23 is at rest, the compressor 31 is also at rest (the same will apply hereinafter).

Subsequently, if the temperatures detected by the inflow water temperature sensor 28 and the outflow hot water temperature sensor 29 are higher than the predetermined value T3, then the control device 70 proceeds to step S8 to determine whether a predetermined backflow determination condition is satisfied. The backflow determination condition will be discussed later. If it is determined that the backflow determination condition is not currently satisfied, then the control device 70 returns to a different control operation.

In the state in which the water pump 23 is at rest, if the temperature detected by the inflow water temperature sensor 28 or the outflow hot water temperature sensor 29 decreases to or below the predetermined value T3 due to, for example, a decrease of the outside air temperature, then the control device 70 proceeds from step S7 to step S9 to start the operation of the water pump 23. As the water pump 23 is operated, the water for hot water supply at the lower part of the hot water storage tank 10 is taken out into the inflow pipe 21 and circulated in the hot water supply circuit 20 such that the water for hot water supply is led into the water flow passage 42 of the water heat exchanger 40 via the inflow water pipe 22 and the outflow water pipe 24 and then moved back to the upper part in the hot water storage tank 10 via the hot water outflow pipe 26 and the outflow pipe 27.

Subsequently, the control device 70 determines in step S10 whether a predetermined time t1 has elapsed, and if the predetermined time t1 has not yet elapsed, then the control device 70 continues the state. After continuing the operation of the water pump 23 for the predetermined time t1, the control device 70 proceeds from step S10 to step S11 to determine whether the temperature detected by the inflow water temperature sensor 28 is lower than the predetermined inflow water temperature T2 described above. If it is determined in step S11 that the temperature detected by the inflow water temperature sensor 28 is the inflow water temperature T2 or higher, then the control device 70 proceeds to step S18 to stop the water pump 23.

Meanwhile, if it is determined in step S11 that the temperature detected by the inflow water temperature sensor 28 is lower than the inflow water temperature T2, then the control device 70 proceeds to step S12 to determine whether a predetermined time t2 has elapsed. Further, the state in which the temperature detected by the inflow water temperature sensor 28 is lower than the inflow water temperature T2 in step S11 lasts for the predetermined time t2 in step S12, then the control device 70 proceeds to step S13 to start the operation of the compressor 31 and the air blower 34 (the operation of the water pump 23 being continued). In other words, if the temperature detected by the inflow water temperature sensor 28 does not reach the inflow water temperature T2 or higher even after the water pump 23 is operated for the predetermined time t1+t2, then the control device 70 starts the boiling operation described above.

Subsequently, the control device 70 determines in step S14 whether the temperature of the water for hot water supply in the inflow water pipe 22 detected by the inflow water temperature sensor 28 has reached the inflow water temperature T2 or higher, and if the temperature is lower than the inflow water temperature T2, then the control device 70 continues the boiling operation. Thereafter, if the temperature detected by the inflow water temperature sensor 28 reaches the inflow water temperature T2 or higher, then the control device 70 proceeds from step S14 to step S15 to stop the compressor 31 and the air blower 34 (while the operation of the water pump 23 continues).

Subsequently, the control device 70 proceeds to step S16 to determine whether the temperature of the water for hot water supply in the hot water outflow pipe 26 on the hot water outflow side of the water heat exchanger 40 detected by the outflow hot water temperature sensor 29 has decreased to or below the temperature of the water for hot water supply in the inflow water pipe 22 on the water inflow side of the water heat exchanger 40 detected by the inflow water temperature sensor 28. If the temperature detected by the outflow hot water temperature sensor 29 is higher than the temperature detected by the inflow water temperature sensor 28, then the control device 70 continues the operation of the water pump 23 without interruption and recovers, in the same manner described above, the heat of the water heat exchanger 40 after the compressor 31 stops.

Thereafter, if the temperature detected by the outflow hot water temperature sensor 29 decreases to or below the temperature detected by the inflow water temperature sensor 28, then the control device 70 proceeds to step S6 to stop the water pump 23 and terminates the antifreeze operation. Thus, if the temperature detected by the inflow water temperature sensor 28 or the outflow hot water temperature sensor 29 decreases to or below the predetermined value T3, then the water for hot water supply is circulated into the hot water supply circuit 20, and if the temperature of the water for hot water supply is low, then the boiling operation is also carried out, thereby preventing the water for hot water supply in the inflow pipe 21 or the outflow pipe 27 from freezing.

(10) Determination of a Backflow

In the case where the heating unit 50 is installed on the roof of a house and the tank unit 60 is installed in the basement, as in the embodiment, the heating unit 50 is located at a position that is higher than the position of the hot water storage tank 10 of the tank unit 60. Hence, if the outside air temperature decreases in a winter season or the like, causing the temperature of the water for hot water supply in the outflow pipe 27 to decrease while the water pump 23 is in a stopped state, then the high-temperature water for hot water supply (hot water) at the upper part in the hot water storage tank 10 flows back into the outflow pipe 27 due to a difference in density as described above. The same applies to the right-angled piping.

The high-temperature water for hot water supply that has entered the outflow pipe 27 eventually enters the heating unit 50 and reaches the inflow water pipe 22 via the hot water outflow pipe 26, the water flow passage 42, the outflow water pipe 24 and the water pump 23, and the temperature thereof will also increase, so that the temperatures detected by the outflow hot water temperature sensor 29 and the inflow water temperature sensor 28, which detect the temperatures of the water for hot water supply in the hot water outflow pipe 26 and the inflow water pipe 22 will not decrease to or below the foregoing predetermined value T3.

Therefore, the procedure does not proceed to step S9 from step S7 of the flowchart of FIG. 3, and hence the antifreeze operation will not be carried out. However, the temperature does not increase up to the inflow pipe 21, so that if the outside air temperature decreases in a winter season or the like, the water for hot water supply in the inflow pipe 21 will eventually inconveniently freeze. For this reason, according to the embodiment, it is determined in step S8 whether the backflow phenomenon is taking place even if the temperatures detected by the inflow water temperature sensor 28 and the outflow hot water temperature sensor 29 do not decrease to or below the predetermined value T3 in step S7 of the flowchart of FIG. 3.

(10-1) Backflow Determination Condition

The backflow phenomenon can be detected in terms of a change in temperature of the water for hot water supply in the heating unit 50. More specifically, when a previous boiling operation or antifreeze operation is terminated (the compressor 31 stops and then the water pump 23 stops), the temperatures detected by the inflow water temperature sensor 28 and the outflow hot water temperature sensor 29 will decrease. However, if the high-temperature water for hot water supply flows back into the outflow pipe 27 while the water pump 23 is in the stopped state, then the temperatures detected by the inflow water temperature sensor 28 and the outflow hot water temperature sensor 29 that have temporarily decreased will switch to increase.

Therefore, the backflow determination condition in the case of the present embodiment is defined as follows:

-   -   (i) The water pump 23 is at rest.     -   (ii) The temperature detected by the inflow water temperature         sensor 28 or the outflow hot water temperature sensor 29 has         increased by a predetermined value or more.

The foregoing condition described in (ii) may alternatively be that the temperature detected by the inflow water temperature sensor 28 or the outflow hot water temperature sensor 29 has temporarily decreased and then switched to increase by a predetermined value or more.

(10-2) Operation when the Backflow Determination Condition is Satisfied

If it is determined in step S7 of the flowchart of FIG. 3 that the temperature detected by the inflow water temperature sensor 28 or the outflow hot water temperature sensor 29 is higher than the predetermined value T3, then the control device 70 proceeds to step S8 and determines that high-temperature water for hot water supply is flowing back into the outflow pipe 27 if the foregoing backflow determination conditions (i) and (ii) have been determined and all the conditions (i) and (ii) are satisfied, and proceeds from step S8 to step S9 to start the operation of the water pump 23. Thereafter, step S10 to step S18 are carried out to perform the foregoing antifreeze operation so as to circulate the water for hot water supply in the hot water supply circuit 20 by the water pump 23. If the temperature remains low after performing the operation for the predetermined time (t1+t2), then the compressor 31 is also operated to heat the water for hot water supply in the same manner as the boiling operation.

Thus, the control device 70 carries out the antifreeze operation, in which the water pump 23 is operated if the temperature of the water for hot water supply of the hot water supply circuit 20 positioned in the heating unit 50, i.e., the temperature detected by the inflow water temperature sensor 28, which detects the temperature of the water for hot water supply on the water inflow side of the water heat exchanger 40, or the temperature detected by the outflow hot water temperature sensor 29, which detects the temperature of the water for hot water supply on the hot water outflow side of the water heat exchanger 40 in the embodiment, decreases to the predetermined value T3 or lower. Further, the control device 70 operates the water pump 23 if the temperature of the water for hot water supply of the hot water supply circuit 20 positioned in the heating unit 50, i.e. the temperature detected by the inflow water temperature sensor 28 or the outflow hot water temperature sensor 29 in the embodiment, increases while the water pump 23 is in the stopped state. Thus, if the phenomenon of backflow of the high-temperature water for hot water supply (hot water) from the hot water storage tank 10 occurs in the hot water supply circuit 20, then the water for hot water supply can be circulated in the hot water supply circuit 20 by operating the water pump 23.

This arrangement makes it possible to prevent the inconvenience in which the backflow phenomenon disables the execution of the antifreeze operation, and the water for hot water supply in the inflow pipe 21 of the hot water supply circuit 20 freezes, the backflow phenomenon frequently taking place in the case where the heating unit 50 is disposed at a higher position than the tank unit 60 or in the case of the right-angled piping, wherein a part of the inflow pipe 21 and the outflow pipe 27 of the hot water supply circuit 20 is placed at a higher position than the tank unit 60, as in the embodiment. In addition, there is no need to provide the outflow pipe 27 of the hot water supply circuit 20 with a check valve or the like, thus preventing an increase in cost attributable to an increase of the number of components.

As described above, if the control device 70 operates the water pump 23 in the case where the temperature of the water for hot water supply of the hot water supply circuit 20 positioned in the heating unit 50 (the temperature detected by the inflow water temperature sensor 28 or the outflow hot water temperature sensor 29) temporarily decreases and then switches to increase while the water pump 23 is in the stopped state, then the occurrence of the backflow phenomenon that takes place after the water pump 23 stops can be accurately determined.

Further, if the temperature of the water for hot water supply on the inflow side of the water heat exchanger 40 (the temperature detected by the inflow water temperature sensor 28) remains the predetermined low value (a value that is lower than the inflow water temperature T2) even after the control device 70 operates the water pump 23 for the predetermined time (t1+t2) in the antifreeze operation as in the embodiment, then the prevention of freezing of the hot water supply circuit 20 can be further smoothly accomplished by operating the compressor 31. According to the embodiment, however, the control device 70 carries out the antifreeze operation also when the temperature of the water for hot water supply of the hot water supply circuit 20 positioned in the heating unit 50 (the temperature detected by the inflow water temperature sensor 28 or the outflow hot water temperature sensor 29 in the embodiment) increases while the water pump 23 is in the stopped state. Therefore, the freezing of the inflow pipe 21 of the hot water supply circuit 20 in the case of the occurrence of the backflow phenomenon can be further securely prevented.

(10-3) Backflow Determination Condition 2

The backflow determination condition is not limited to the one described above, and may alternatively be as follows:

-   -   (i) The water pump 23 is at rest.     -   (ii) The temperature detected by the inflow water temperature         sensor 28 or the outflow hot water temperature sensor 29         increases by a predetermined value or more within a         predetermined time.

The foregoing condition (ii) may be a condition in which the temperature detected by the inflow water temperature sensor 28 or the outflow hot water temperature sensor 29 temporarily decreases and then switches to increase by a predetermined value or more within the predetermined time.

Further, if the control device 70 is adapted to proceed to step S9 when all the foregoing conditions (i) and (ii) are satisfied, then the occurrence of the backflow phenomenon can be further accurately determined without being influenced by disturbance.

(10-4) Backflow Determination Condition 3

Further, the backflow determination condition may be as follows:

-   -   (i) The water pump 23 is at rest.     -   (ii) The temperature detected by the inflow water temperature         sensor 28 or the outflow hot water temperature sensor 29         increases by a predetermined value or more (Condition (ii) may         be that the temperature detected by the inflow water temperature         sensor 28 or the outflow hot water temperature sensor 29         temporarily decreases and then switches to increase by the         predetermined value or more).     -   (iii) The outside air temperature detected by the outside air         temperature sensor 55 is equal to or lower than a predetermined         value (a predetermined value that is lower than the         predetermined value T3 and greater than the freezing point; e.g.         2° C.)

If the control device 70 is adapted to proceed to step S9 when all the foregoing conditions (i) to (iii) are satisfied, then the backflow phenomenon in a low outside air temperature environment can be accurately detected, thus making it possible to avoid an unnecessary operation of the water pump 23.

(10-5) Backflow Determination Condition 4

Further, the backflow determination condition may be as follows:

-   -   (i) The water pump 23 is at rest.     -   (ii) The temperature detected by the inflow water temperature         sensor 28 or the outflow hot water temperature sensor 29         increases by a predetermined value or more within a         predetermined time (Condition (ii) may be that the temperature         detected by the inflow water temperature sensor 28 or the         outflow hot water temperature sensor 29 temporarily decreases         and then switches to increase by the predetermined value or more         within a predetermined time).     -   (iii) The outside air temperature detected by the outside air         temperature sensor 55 is equal to or lower than a predetermined         value (a predetermined value that is lower than the         predetermined value T3 and greater than the freezing point; e.g.         2° C.)

If the control device 70 is adapted to proceed to step S9 when all the foregoing conditions (i) to (iii) are satisfied, then the backflow phenomenon in a low outside air temperature environment can be accurately detected, thus making it possible to avoid an unnecessary operation of the water pump 23.

The above has described preferred embodiments of the present invention. However, the present invention is not limited to the foregoing embodiments, and various other changes and modifications can be made on the basis of the technical concept of the present invention.

DESCRIPTION OF REFERENCE NUMERALS

-   -   1 heat pump type hot water supplying device     -   10 hot water storage tank     -   16 stored hot water temperature sensor     -   20 hot water supply circuit     -   21 inflow pipe     -   22 inflow water pipe     -   23 water pump     -   24 outflow water pipe     -   26 hot water outflow pipe     -   27 outflow pipe     -   28 inflow water temperature sensor     -   29 outflow hot water temperature sensor     -   30 heat pump circuit     -   31 compressor     -   32 evaporator     -   33 expansion valve     -   34 air blower     -   40 water heat exchanger     -   41 refrigerant flow passage     -   42 water flow passage     -   50 heating unit     -   55 outside air temperature sensor     -   60 tank unit     -   70 control device 

1. A heat pump type hot water supplying device comprising: a heating unit provided with a heat pump circuit formed by connecting a compressor, a water heat exchanger, a decompressor and an evaporator; a tank unit provided with a hot water storage tank for storing water for hot water supply; a hot water supply circuit in which the water for hot water supply in the hot water storage tank is taken out from a lower part of the hot water storage tank by a water pump, circulated into the water heat exchanger and led into an upper part of the hot water storage tank; and a control device which carries out a boiling operation for heating, by a refrigerant, the water for hot water supply, which circulates through the water heat exchanger, by operating the water pump and the compressor, wherein the control device carries out an antifreeze operation, in which the water pump is operated, in the case where the temperature of the water for hot water supply in the hot water supply circuit positioned in the heating unit decreases to a predetermined value or lower, and operates the water pump in the case where the temperature of the water for hot water supply in the hot water supply circuit positioned in the heating unit increases while the water pump is in a stopped state.
 2. The heat pump type hot water supplying device according to claim 1, wherein the control device operates the water pump in the case where the temperature of the water for hot water supply in the hot water supply circuit positioned in the heating unit temporarily decreases and then switches to increase while the water pump is in a stopped state.
 3. The heat pump type hot water supplying device according to claim 1, wherein the control device operates the water pump in the case where the temperature of the water for hot water supply in the hot water supply circuit positioned in the heating unit increases by a predetermined value or more within a predetermined time while the water pump is in a stopped state.
 4. The heat pump type hot water supplying device according to claim 1, wherein the control device operates the water pump in the case where an outside air temperature is a predetermined value or lower and the temperature of the water for hot water supply in the hot water supply circuit positioned in the heating unit increases while the water pump is in a stopped state.
 5. The heat pump type hot water supplying device according to claim 1, wherein the control device operates the compressor in the case where the temperature of the water for hot water supply on an inflow side of the water heat exchanger is a predetermined low value despite the water pump having been operated for a predetermined time in the antifreeze operation.
 6. The heat pump type hot water supplying device according to claim 5, wherein the control device carries out the antifreeze operation in the case where the temperature of the water for hot water supply in the hot water supply circuit positioned in the heating unit increases while the water pump is in a stopped state.
 7. The heat pump type hot water supplying device according to claim 1, wherein the temperature of the water for hot water supply in the hot water supply circuit positioned in the heating unit is the temperature of the water for hot water supply on the inflow side of the water heat exchanger or the temperature of the water for hot water supply on the hot water outflow side of the water heat exchanger.
 8. The heat pump type hot water supplying device according to claim 1, wherein the heating unit is disposed at a position that is higher than the position of the tank unit.
 9. The heat pump type hot water supplying device according to claim 1, wherein the hot water supply circuit has an inflow pipe, which is positioned between the heating unit and the tank unit to take out the water for hot water supply in the hot water storage tank from the lower part of the hot water storage tank, and an outflow pipe for passing the water for hot water supply, which has circulated through the water heat exchanger, into the upper part of the hot water storage tank, and at least a part of the inflow pipe and the outflow pipe is provided at a position that is higher than the position of the tank unit. 